Summary report on new regulatory codes and criteria and guidelines : IAEA guidelines for WWER reactor coolant system integrity assessment

In the frame of the nuclear safety programme to assist the countries of Central and Eastern Europe, the IAEA identified and ranked in total 263 safety issues for WWER-440/230, WWER-440/213 and WWER-1000/320 nuclear power plants, related to both design and operation. In the area of reactor coolant system integrity, 24 safety issues were identified and 15 of them ranked as of high safety significance. These include: reactor pressure-vessel integrity and related aspects, primary and secondary high-energy piping integrity, steam generator integrity and reliability of the non-destructive testing for in-service inspection. In addition to obtaining international consensus on possible solutions to address the safety issues identified and to reviewing completeness of proposed safety improvements, the IAEA initiated development of guidelines to address the issues of highest safety concern. In the area of the reactor coolant system integrity, guidelines for the leak before break concept application, for the pressurized thermal shock analysis and for the in-service inspection systems qualification were developed. Further activities of the IAEA were focused on the implementation of guidelines developed in the Member States concerned. With this objective, a Co-ordinated Research Programme 'Round-robin Exercise on WWER-440 Reactor Pressure Vessel Embrittlement, Annealing and Re-embrittlement', a WWER-440/213 Pressurized Thermal Shock Analysis Benchmark Exercise' and a pilot study to implement the qualification approach to a real power plant component have been initiated by the IAEA and are well under way at present. In this paper, an overview of these IAEA activities related to reactor coolant system integrity is provided and the main principles and elements of guidelines developed discussed.